The most commercially successful supercharger arrangement for diesel engines to date is the type generally referred to as an aerodynamic wave machine in U.S. Pat. No. 2,853,987 and as the COMPREX (registered trademark of BBC Brown, Boveri & Co., Ltd., Baden, Switzerland), as described in a paper by Peter K. Doerfler, entitled "Comprex Supercharging of Vehicle Diesel Engines" presented at the Automotive Engineering Congress and Exposition in Detroit, Mich., Feb. 24-28, 1975. The basic principle of that supercharger is the transfer of pressure energy from high pressure engine exhaust gas to low pressure air which is then delivered at high pressure back to the engine. The wave machine includes a cylindrical chamber in which there is located a rotor with multiple radial vanes, the rotor being driven by a belt pick off from the engine. Openings are provided at the cylinder ends at appropriate locations to effect ingress and egress of fluid to and from the chamber. In operation, atmospheric air, present in the spaces between adjacent rotating vanes, experiences a pressure wave when it passes an inlet opening at one of the chambers to which the high pressure engine exhaust gas is directed. The compression wave, moving at the speed of sound, compresses the air as the wave passes by. The compressed air behind the wave occupies less space than before, permitting the engine exhaust gas to enter into the space between the vanes. As the compression wave reaches the opposite end of the cylinder, the vanes in question pass an outlet opening in that end which permits the compressed air to egress to the engine intake. By the time the compression wave reflects back toward the exhaust gas supply end of the chamber, the vanes have moved past the exhaust gas supply opening. Eventually the still slightly pressurized exhaust gas is permitted to egress from another chamber opening to ambient as the vanes pass the latter opening. A still further opening admits air into the space between the vanes before the rotation cycle is completed.
The aforementioned wave machine thus serves as a supercharger for the engine by utilizing the pressurized hot engine exhaust gases to perssurize the cold air delivered to the engine. The system is relatively efficient and has been used for a number of years. Nevertheless, there are some problems associated with the wave machine which have served as limiting factors on its increased utilization. Specifically, the wave machine requires additional controls during cold engine start up conditions because the exhaust gas flows straight through the machine to the engine intake under low engine RPM conditions. These controls usually take the form of a manually operated choke-like arrangement which moves a butterfly valve or the like in position to admit air into the engine from a source other than the wave machine. In addition, the wave machine has a rotor arrangement which is subject to temperature variations on the order of 800.degree. C., thereby limiting the choice of materials that can be used and still maintain the critical dimensional tolerances necessary to keep the engine operating. Further, because of the complex moving parts and their critical tolerances, wear and tear and a continuing need for lubrication present significant problems. Still further, because of the relative complexity of the machine, the cost becomes a problem, particularly when the machine is used in conjunction with a passenger vehicle. Another problem relates to the fact that the wave machine must be driven by the engine, resulting in power loss and a limitation on the frequency of cyclic wave machine operation. The need to drive the wave machine from the engine also subjects the engine to being smothered by its exhaust gas if a drive belt breaks and also requires the wave machine to be located near the engine which often presents a severe space problem to a vehicle designer.
It is an object of the present invention to provide a supercharger method and apparatus in which the aforementioned problem and disadvantages are obviated without sacrificing engine performance.
It is also an object of the present invention to provide an apparatus and method for efficiently and economically transferring energy from one fluid to another, wherein the fluids may be liquid or gas.